CONTROLLING ADSORBATE INTERACTIONS FOR ADVANCED CHEMICAL PATTERNING

Open Access
Author:
Saavedra Garcia, Hector Miguel
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
January 08, 2010
Committee Members:
  • Paul S Weiss, Dissertation Advisor
  • Paul S Weiss, Committee Chair
  • Albert Welford Castleman Jr., Committee Member
  • Thomas E Mallouk, Committee Member
  • Vincent Henry Crespi, Committee Member
Keywords:
  • molecular exchange
  • chemical patterning
  • soft lithography
  • scanning tunneling microscopy
  • self assembled monolayers
  • cluster assembled materials
  • microcontact printing
Abstract:
Molecules designed to have specific interactions were used to influence the structural, physical, and chemical properties of self-assembled monolayers. In the case of 1 adamantanethiolate monolayers, the molecular structure influences lability, enabling alkanethiol molecules in solution to displace the 1 adamantanethiolate monolayers, ultimately leading to complete molecular exchange. The similar Au-S bond environments measured for both n alkanethiolate and 1 adamantanethiolate monolayers indicate that displacement is not a result of weakened Au−S bonds. Instead, it was hypothesized that the density differences in the two monolayers provide a substantial enthalpic driver, aided by differences in van der Waals forces, ultimately leading to complete displacement of the 1 adamantenthiol molecules. Additionally, it was discovered that displacement occurs via fast insertion of n dodecanethiolate at the defects in the original 1-adamantanethiolate monolayer, which nucleates an island growth phase and is followed by slow ordering of the n dodecanethiolate domains into a denser and more crystalline form. Langmuir-based kinetics, which describe alkanethiolate adsorption on bare Au{111}, fail to model this displacement reaction. Instead, a model of perimeter-dependent island growth yields good agreement with kinetic data over a 100-fold variation in n dodecanethiol concentration. Rescaling the growth rate at each concentration collapses all the data onto a single universal curve, suggesting that displacement is a scale-free process. Exploiting the knowledge gained by studying 1-adamantethiolate monolayer displacement, a reversible molecular resist was developed, in which displacement is controlled via external stimuli. This methodology for the fabrication of controllably displaceable monolayers relies on carboxyl functionalized self assembled monolayers and in situ Fischer esterification. Using an 11 mercaptoundecanoic acid monolayer as a model system, it was shown that in situ esterification results in the creation of subtle chemical and structural defects that promote molecular exchange reactions to go to completion. The complementary hydrolysis reaction can be employed to quench the reacted monolayer, significantly hindering further displacement. The generality of reversible lability was tested by applying the in-situ esterification reaction to the structurally distinct carboxyl functionalized molecule 3-mercapto-1-adamantane-carboxylic acid. In addition to the studies of manipulating the interactions in self-assembled monolayers, materials with tunable optical and electronic properties were fabricated using atomic clusters as building blocks. It was shown that materials assembled from the same cluster motif, in this case 〖As〗_7^(3-), can result in materials with band gaps that vary predictably between 1.09 to 2.08 eV. The size and highest occupied molecular orbital of the alkali metal counter-cation used in the assembly was shown to affect the band gap of the cluster-assembled solids. Furthermore, the dimensionality of the cluster-cluster interactions played a crucial role in determining the resulting properties. These results demonstrate how complex surface assemblies, or novel solid materials, can be fabricated by manipulating the interactions between the individual components within the assemblies, paving the way for the fabrication of next-generation devices and materials.